Matched filter simultaneously operating for two different type codes

ABSTRACT

In a matched filter, a plurality of data holding circuits adapted to sequentially hold a plurality of straight binary data and a plurality of correlators are provided. Each of the correlators receiving one bit of a known code and one bit of a selected code as a 2-bit code outputs the straight binary data as it is when the 2-bit code is “00”, outputs the straight binary data after logically inverting when the straight binary data when the 2-bit code is “11”, and outputs exclusive OR values between the straight binary data except for its most significant bit and the most significant bit while outputting “1” for the most significant bit when the 2-bit code is one of “01” and “10”. Also, an adder adds output signals of the correlators and outputs an addition result as a correlation value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a matched filter used in a code division multiple access (CDMA) receiver for determining the correlation between input data and scrambling codes.

2. Description of the Related Art

Generally, a CDMA transmission/reception system is adapted to multiple access, using scrambling/descrambling operation, a plurality of scrambling codes and carrier waves of the same frequency. This will be explained later in detail.

With the CDMA transmission/reception system, however, a receiver cannot correctly carry out a descrambling operation if it misses the right timing of scrambling operation carried out by a base station.

Additionally, since each base station has a plurality of scrambling codes it uses, the receiver cannot know in advance the scrambling code being used by the base station to be accessed by the receiver. However, if the receiver cannot get any information from the base station, the receiver cannot access the base station unless it can specifically know the scrambling code that the base station uses.

A perch function using a matched filter is used to solve the above-mentioned problem. This also will be explained later in detail.

A prior art matched filter is accompanied by the following problems. The operation of obtaining the scrambling timing and that of identifying a scrambling code being used by the base station are carried out independently at different timings, so that a discrepancy in the correlating timing and, in the worst case, a total incapability of signal reception can occur. Also, half of the power used for receiving the codes is consumed for nothing.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a matched filter that can carry out an operation of obtaining the timing of a base station by using a known scrambling code contained in a long code mask symbol and an operation of determining if a selected scrambling code agrees with a scrambling code contained in the logic symbol.

According to the present invention, in a matched filter, a plurality of data holding circuits adapted to sequentially hold a plurality of straight binary data and a plurality of correlators are provided. Each of the correlators receiving one bit of a known code such as a known scrambling code and one bit of a selected code such as a scrambling code selected by a base station as a 2-bit code, outputs the straight binary data as it is when the 2-bit code is “00”, outputs the straight binary data after logically inverting the straight binary data when the 2-bit code is “11”, and outputs exclusive OR values between the straight binary data except for its most significant bit and the most significant bit while outputting “1”for the most significant bit when the 2-bit code is one of “01” and “10”. Also, an adder adds output signals of the correlators and outputs an addition result as a correlation value.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from the description as set forth below, as compared with the prior art, with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit diagram illustrating a first prior art CDMA transmission/reception system;

FIG. 2 is a circuit diagram illustrating a second prior art CDMA transmission/reception system;

FIGS. 3A through 3D are data formats showing a data structure of a perch channel through which the perch search section of FIG. 2 receives signals;

FIG. 4 is a circuit diagram of the matched filter of the system of FIG. 2;

FIG. 5 is a circuit diagram illustrating an embodiment of the matched filter according to the present invention;

FIG. 6 is a circuit diagram of the correlator of FIG. 5; and

FIGS. 7A, 7B and 7C are is a graphs showing the output characteristics of the matched filter of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before the description of the preferred embodiments, prior art CDMA transmission/reception systems will be explained with reference to FIGS. 1 through 4.

In FIG. 1, which illustrates a first prior art CDMA transmission/reception system, reference numerals 101 and 102 designate base stations, particularly, transmitters thereof, and 103 and 104 designate mobile stations, particularly, receivers thereof. The transmitter 101 scrambles a logic symbol LS_(a) by a scrambler 1011 using a scrambling code SC_(a) and transmits it by a carrier wave from an antenna 1012. Similarly, the transmitter 102 scrambles a logic symbol LS_(b) by a scrambler 1021 using a scrambling code SC_(b) and transmits it by a carrier wave from an antenna 1022. In this case, the frequency of the carrier wave of the transmitter 101 is the same as that of the transmitter 102. Also, the transmission rate of scrambling codes is normally tens to several hundreds of times of that of logic symbols.

The receiver 103 receives the carrier waves from the transmitters 101 and 102 from an antenna 1031 and descrambles the carrier waves by a descrambler 1032 using the scrambling code SC_(b) to take out the logic symbol LS_(b). Similarly, the receiver 104 receives the carrier waves from the transmitters 101 and 102 from an antenna 1041 and descrambles the carrier waves by a descrambler 1042 using the scrambling code SC_(a) to take out the logic symbol LS_(a).

Thus, the CDMA transmission/reception system of FIG. 1 is adapted to multiple access, using scrambling/descrambling operation, a plurality of scrambling codes and carrier waves of the same frequency.

With the CDMA transmission/reception system of FIG. 1, however, the receiver 103 or 104 cannot correctly carry out a descrambling operation if it misses the right timing of scrambling operations carried out by the transmitter 102 or 101 If the scrambling timing of the receivers 103 or 104 is deviated even by a single chip (time period for several bits of data), the receiver 103 or 104 can no longer receive the signal transmitted from the transmitter 102 or 101 at all. Particularly, with a wide band CDMA (W-CDMA) transmission/reception system that belongs to the category of CDMA, no base stations (transmitters) synchronize their output signals and, therefore, a receiver sequentially has to try to synchronize its signal receiving operation with the signal of one base station it receives each time it switches from one base station to another.

Additionally, since each base station has a plurality of scrambling codes it uses, the receiver cannot know in advance the scrambling code being used by the base station to be accessed by the receiver. For example, a W-CDMA type transmission/reception system is adapted to use a total of 32 scrambling codes and there is no way for the receiver to know in advance the scrambling code that the base station uses. However, if the receiver cannot get any information from the base station, the receiver cannot access the base station unless it can specifically know the scrambling code that the base station is using.

A perch function is used to solve the above-mentioned problem. With a perch function, the receiver can obtain information from the base station on the scrambling codes and the timings that the base station uses for scrambling logic symbols. Then, the receiver can obtain information on the scrambling codes and so on from the base station by carrying out a perch search operation by means of the perch function.

In FIG. 2, which illustrates a second prior art CDKA transmission/reception system, reference numeral 201 designates a base station, particularly, a transmitter thereof, and 202 designates a mobile station.

The transmitter 201 is constructed by two scramblers 2011 and 2012, an adder 2013, and an antenna 2014. The adder 2013 adds a signal obtained by scrambling a logic symbol LS by means of the scrambler 2011 using a known scrambling code SC₁ to a signal obtained by scrambling the same logic symbol LS means of the scrambler 2012 using an unknown scrambling code SC₂ that the transmitter 201 uses out of the 32 scrambling codes. Then, the signal obtained by addition as a long code mask symbol is transmitted from the antenna 2014. Note, that the two scrambling codes SC₁ and SC₂ of different types are started at the same timing, and the logic symbols are identical before they are scrambled.

The mobile station 202 is constructed by a ratio frequency/intermediate frequency (RF/IF) section 2021, a transmitting section 2022, a receiving section 2023, and an antenna 2024.

The transmitting section 22 outputs to the RF/IF section 2021 a base band signal to be transmitted to the base station 201.

The RF/IF section 2021 modulates the carrier wave by means of the base band signal output from the transmitting section 2022 and transmits the modulated carrier wave from the antenna 2024 to the base station 201. It also demodulates the signal transmitted via the antenna 2024 from the base station 201 and outputs the demodulated signal to the receiving section 2023.

The receiving section 2023 is constructed by a perch search section 2024, a search section 2025, finger receiving sections 2026 and a rake receiving section 2027.

The perch search section 2024 obtains various pieces of information on the base station 201 from the base band signal demodulated by the RF/IF section 2021 and outputs them to the downstream-side circuit. The perch search section

The search section 2025 detects the difference between the timing of the direct wave and the reflected wave due to the multipath component of the base band signal.

The finger receiving sections 2026 correct the difference in the timing between different signals by delaying the base band signal as a function of the difference of the timing detected by the search section 2025.

The rake receiving section 2027 synthetically combines the signals received by the finger receiving sections 2026 at an optimum ratio and outputs the synthesized signal to the downstream-side circuit.

FIGS. 3A through 3D are data formats showing a data structure of a perch channel through which the perch search section 2024 receives signals.

As shown in FIG. 3A, a perch channel 30 is one of a number of 640 msec super frames. Also, as shown in FIG. 3B, the perch channel 30 is formed by 64 ratio frames 31 ₁ through 316 ₄ for transmitting information on each of the related receivers.

As shown in FIG. 3C, the ratio frame 31-1 is formed by time slots 32 ₁ through 32 ₁₄, of which the time slot 32 ₁ is formed by a pilot symbol 33, a broadcast channel (BCCH) symbol 34 and a long code mask symbol 35, as shown in FIG. 3D.

Note that 1 bit of a logic symbol is scrambled to 256 chips in FIGS. 3A through 3D in order to illustrate a W-CDMA transmission/reception system where the scrambling code has a length of 256 chips.

The long code mask symbol 35 is produced by adding a signal obtained by scrambling a 1-bit logic symbol by means of the scrambler 2011 using a known scrambling code SC₁ and a signal obtained by scrambling the same logic symbol by means of the scrambler 2012 using an unknown scrambling code SC₂.

The receiver 2123 firstly gets the scrambling timing from the long code mask symbol 35 as shown in FIG. 3D and detects the unknown scrambling code being used by the base station 201 by using the scrambling timing. For this purpose the matched filter 2024 a is provided in the perch search section 2024.

In FIG. 4, which is a circuit diagram of the matched filter 2024 a of FIG. 2, the matched filter 2024 a is constructed by dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆, exclusive NOR circuits 2 ₁ through 2 ₂₅₆ exclusive NOR circuits 3 ₁ through 3 ₂₅₆ and adders 4 and 5.

The matched filter 2024 a firstly transforms a received base band signal into an input data IN of a straight binary signal with a bit width of 8 bits by an analog/digital (A/D) converter (not shown).

Then, the dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆ sequentially hold the 8-bit input data IN on a chip rate basis.

The exclusive NOR circuits 2 ₁ through 2 ₂₅₆ determine exclusive NORs of the 8-bit input data IN held by the 93 respective dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆ and the respective known scrambling codes 6 ₁ through 6 ₂₅₆ (SC₁).

The exclusive NOR circuits 3 ₁ through 3 ₂₅₆ determine exclusive NORs of the 8-bit input data IN held by the respective dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆ and selected respective scrambling codes 7 ₁ through 7 ₂₅₆ (SC₂′).

The adder 4 adds the outputs of the exclusive NOR circuits 2 ₁ through 2 ₂₅₆ and outputs the addition result as a correlation value COR₁.

On the other hand, the adder 5 adds the outputs of the exclusive NOR circuits 3 ₁ through 3 ₂₅₆ and outputs the addition result as a correlation value COR₂.

Now, the operation of the matched filter 2024 a of FIG. 4 will be explained below.

Firstly, the matched filter 2024 a uses the known scrambling codes 6 ₁ through 6 ₂₅₆ and determines the scrambling timing of the base station from which it is going to receive signals.

The input data that has been transformed into an 8-bit signal is held sequentially and commonly by the dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆ and the exclusive NOR circuits 2 ₁ through 2 ₂₅₆ determine the exclusive NORs of the signal and the known respective scrambling codes 6 ₁ through 6 ₂₅₆.

While only the operation of the exclusive NOR circuit 2 ₁ is described here, the description applies to all the exclusive NOR circuits 2 ₁ through 2 ₂₅₆ and the remaining exclusive NOR circuits 2 ₂ through 2 ₂₅₆ operate in a similar way.

As a result of the exclusive NOR circuit 2 ₁ determining the above described exclusive NOR, the data held by the dynamic flip-flop circuit 1 ₁ is output when the known scrambling code 6 ₁ is equal to “1” whereas the data held by the dynamic flip-flop circuit 1 ₁ is logically inverted before it is output when the known scrambling code 6 ₁ is equal to “0”.

Then, the adder 4 adds all the outputs of the exclusive NOR circuits 2 ₁ through 2 ₂₅₆ and outputs the addition result as an obtained correlation value COR₁. If the obtained correlation value COR shows a large value, it means that the input data IN and the known scrambling codes 6 ₁ through 6 ₂₅₆ agree with each other, so that the receiver can use the obtained timing as the scrambling timing of the base station.

Then, the matched filter 2024 a selects one of the scrambling codes that the base station may use and uses it as scrambling codes 7 ₁ through 7 ₂₅₆.

Since the scrambling timing is already known, the matched filter 2024 a selects a start timing on the basis of the scrambling timing and determines the correlation between the selected scrambling codes 7 ₁ through 7 ₂₅₆ and input data in the same manner as described above. More, specifically, it monitors the value of the obtained correlation value COR₂ for the scrambling timing and determines if the obtained correlation value COR₂ shows a large value at the obtained scrambling timing.

If the obtained correlation value COR₂ does not show a large value, it means that the selected scrambling codes 7 ₁ through 7 ₂₅₆ are not the one being used by the base station and hence the matched filter 2024 a selects another scrambling code and uses it as scrambling codes 7 ₁ through 7 ₂₅₆.

If it is confirmed that the obtained correlation value COR₂ shows a large value in synchronization with the scrambling timing obtained by the above operation, then it means that the selected scrambling codes 7 ₁ through 7 ₂₅₆ represent the scrambling code being used by the base station.

It may be appreciated that the unknown scrambling code being used by the base station is detected only after obtaining the scrambling timing by using known scrambling codes 6 ₁ through 6 ₂₅₆ because it is extremely difficult to determine if an obtained correlation is correct or not when neither the scrambling timing nor the identification of the scrambling code being used by the base station are known.

Thus, it is necessary for the matched filter 2024 a of FIG. 4 to obtain the scrambling timing first and, thereafter, select the start timing of the unknown scrambling code being used by the base station.

Additionally, because of the fact that a receiver cannot use a high precision reference oscillator as used by the base station and the moving speed of the receiver is always changing, the correlating timing between the base station and the receiver can come to show a discrepancy over the course of time. The receiver normally has an automatic frequency control (AFC) feature for correcting the error between the basic clock signal of the receiver and that of the base station and the discrepancy in the correlating timing between them. However, since a perch search operation is an initial operation for the receiver to access the base station by way of a ratio wave, an AFC operation cannot be carried out during the perch search operation.

Thus, the scrambling timing obtained by using a known scrambling code can be shifted with time and, during the operation of determining if the selected scrambling code agrees with the scrambling code being used by the base station, the scrambling timing that the receiver is using can be shifted from the actual scrambling timing. Any deviation from the actual scrambling timing results In a reduced reception gain and a degraded performance of the system that can lead to a total incapability of signal reception in the worst case.

Additionally, with the system of FIG. 2, the base station 201 allocates equal transmission power to two scrambling codes SC₁ and SC₂ and the receiver 202 has to determine the correlation for each of them so that half of the power used for receiving the codes is in fact consumed for nothing.

In FIG. 5, which illustrates an embodiment of the matched filter according to the present invention, the exclusive NOR circuits 2 ₁ through 2 ₂₅₆ and 3 ₁ through 3 ₂₅₆ of FIG. 4 are replaced by correlators 8 ₁ through 8 ₂₅₆, and the adders 4 and 5 of FIG. 4 are replaced by a single adder 9.

Each of the correlators 8 ₁ through 8 ₂₅₆ receives the a corresponding one of the known scrambling codes 6 ₁ through 6 ₂₅₆ and one of the selected scrambling codes 7 ₁ through 7 ₂₅₆ as a signal with a 2-bit code value having corresponding bits in combination and then carries out a processing operation on the input signals IN₁ to IN₂ held by the corresponding one of the dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆ on the basis of the scrambling code values such as 6 ₁ and 7 ₁in a manner as will be described below.

FIG. 6 is a detailed circuit diagram of the correlator 8 ₁ of FIG. 5; however, a similar configuration is applied to the other correlators 8 ₂ through 8 ₂₅₆ of FIG. 5.

In FIG. 6, the correlator 8 ₁ is constructed by an inverter circuit section 61, an exclusive OR circuit section 62 and a selector 63. That is, the input signals IN₁ through IN₈ are supplied as an 8-bit signal S_(A) to the selector 63. On the other hand, the inverter circuit section 61 receives the input signals IN₁ through IN₈ and transmits its output signal S_(B) to the selector 63, and the exclusive OR circuit section 62 receives the input signals IN₁ through IN₈ and transmits its output signal S_(X) to the selector 63.

Since the signal S_(A) is equal to the combination of the input signals IN₁ through IN₈, the relationship between the input signals IN₁ through IN₈ and the signal S_(A) is as shown in FIG. 7A. Also, since the signal S_(B) is the combination of inverted signals of the input signals IN₁ through IN₈, the relationship between the input signals IN₁ through IN₈, and the signal S_(B) is as shown in FIG. 7B. Further, the signal S_(C) is a combination of exclusive ORs of the input signals IN₁ through IN₇ and the most significant bit input signal IN₈, and a most significant bit V_(CC)(=“1”), the relationship between the input signals IN₁ through IN₈ and the signal S_(C) is as shown in FIG. 7C. In FIG. 7C, the input signals IN₁ through IN₈ are equal to “00” (hexadecimal notation), the signal S_(C) is “80”. The value of the signal S_(C) is increased until the input signals IN₁ through IN₈ reach “0F”. Also, if the input signals IN₁ through IN₈, exceed “80”, the value S_(C) is decreased. Further, if the input signals IN₁ through IN₈ are equal to “FF”, the value of the signal S_(C) is “80”.

The selector 63 selects one of the signals S_(A), S_(B) and S_(C) in accordance with the scrambling codes 6 ₁ and 7 ₁. That is, if (6 ₁, 7 ₁)=(0, 0), the selector 63 selects the signal S_(A) and transmits it as the output signals OUT₁ through OUT₈ to the adder 9. Also, if (6 ₁, 7 ₁)=(1, 1), the selector 63 selects the signal S_(B) and transmits it as the output signals OUT₁ through OUT₈ to the adder 9. Further, if (6 ₁, 7 ₁)=(0, 1), or (1, 0) the selector 63 selects the signal S_(C) and transmits it as the output signals OUT₁ through OUT₈ to the adder 9.

Note that the selector 63 can be easily made by logic circuits and switch circuits.

The adder 9 adds all the output signals from the correlators 8 ₁ through 8 ₂₅₄ and outputs the addition result as an obtained correlation value COR₃.

The operation of the matched filter of FIGS. 5 and 6 including the system of FIG. 2 will be explained next.

Firstly, the perch search section 2024 selects a 35 known scrambling code out the scrambling codes of the two types used for scrambling a long code mask symbol 35 as shown in FIG. 3D and uses it as scrambling codes 6 ₁, through 6 ₂₅₆. Then, the perch search section 2024 selects a scrambling code that the base station may possibly use and uses it as scrambling codes 7 ₁ through 7 ₂₅₆.

Then, an 8-bit input data IN obtained by the A/D conversion of a demodulated base band signal is sequentially held by the dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆.

The input data IN held by the dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆ is then input to the correlators 8 ₁ through 8 ₂₅₆ as an 8-bit signal.

Note that each of the bits of the scrambling codes 6 ₁ through 6 ₂₅₆ and the corresponding one of the bits of the scrambling codes 7 ₁ through 7 ₂₅₆ are combined as an input to the corresponding one of the correlators 8 ₁ through 8 ₂₅₆ as a 2-bit code values

Then, if the code value is “00”, the output signals OUT₁ through OUT₈ will become equal to “FF” that is the largest possible value when the input signals IN₁ through IN₈ are “FF”. If the code value is “11”, the output signals OUT₁ through OUT₈ will also become equal to “FF” that is the largest possible value when the input signals IN₁ through IN₈ are “00”. If the code value is either “01”, or “10”, the output signals OUT₁ through OUT₈ will become equal to “FF” that is the largest possible value when the input signals IN₁ through IN₈ are “7F” or “80”.

Thus, when both the known scrambling codes 6 ₁ through 6 ₂₅₆ and the selected scrambling codes 7 ₁ through 7 ₂₅₆ agree with the scrambling codes of the two types contained in the long code mask symbol 35, the absolute value of the obtained correlation value COR₃, expressed as a complement of 2 will become the largest. If the known scrambling codes 6 ₁ through 6 ₂₅₆ agree with the scrambling codes of the two types contained in the long code mask symbol 35, but the selected scrambling codes 7 ₁ through 7 ₂₅₆ do not agree with the scrambling codes of the two types contained in the long code mask symbol 35, then the absolute value of the obtained correlation value COR₃ expressed as a complement of 2 will not become large or, if it become large, it will not be as large as its counterpart when the two sets of scrambling codes agree with the scrambling codes of the two types. In this way, it is possible to determine if the selected scrambling codes 7 ₁ through 7 ₂₅₆ agree with the scrambling codes contained in the long code mask symbol 35.

Thus, in the above-mentioned embodiment, the scrambling codes of two sets are added and the added value is used to see the correlation value with the input data IN, so that the scrambling timings of the scrambling codes of the two types can be searched for simultaneously.

Also, in the above-mentioned embodiment, only a set of correlators 8 ₁ through 8 ₂₅₆ and an adder 9 are provided. Therefore, it there are 32 different types of scrambling codes that the base station may possibly use, the long code mask symbol 35 will have to be received 32 times in the worst case until the receiver can identify the scrambling code being used by the base station.

However, such a problem can be avoided by providing as many sets of correlators and an adder 8 as the number of types of scrambling codes that the base station may possibly use so that the receiver may well receive the long code mask symbol 35 only once to identify the scrambling code being used by the base station.

In the above-mentioned embodiment while the input data IN is held by the dynamic flip-flop circuits 1 ₁ through 1 ₂₅₆, the present invention is not limited to the use of dynamic flip-flop circuits for holding the input data and any other circuits may alternatively be used if they can hold the input data on a chip rate basis.

Additionally, while an input data IN having a bit width of 8 bits is obtained by the A/D convertion of a base band signal, the present invention is not limited to the use of an 8-bit signal for the input data IN and an input data with a bit width other than 8 bits may also be used for the purpose of the present invention.

As explained hereinabove, according to the present invention, since the scrambling codes of two sets are added and the added value is used to determine the correlation value with the input data IN, the scrambling timings of the scrambling codes of the two types can be searched for simultaneously. Thus, it is possible to effectively prevent any discrepancy in the correlating timing between the base station and the receiver that can lead to a total incapability of signal reception. Additionally, no power will be used for nothing for receiving a signal, because the two operations are carried out simultaneously. 

What is claimed is:
 1. A matched filter comprising: a plurality of data holding circuits adapted to sequentially hold a plurality of straight binary data; a plurality of correlators, each connected to one of said data holding circuits, each of said correlators receiving one bit of a known code and one bit of a selected code as a 2-bit code, outputting said straight binary data as it is when said 2-bit code is “00”, outputting said straight binary data after logically inverting when said straight binary data when said 2-bit code is “11”, and outputting exclusive OR values between said straight binary data except for a most significant bit thereof and said most significant bit while outputting “1” for said most significant bit when said 2-bit code is one of “01” and “10”; an adder, connected to said correlators, for adding output signals of said correlators and outputting an addition result as a correlation value.
 2. The matched filter as set forth in claim 1, wherein each of said data holding circuits comprises a dynamic flip-flop circuit.
 3. The matched filter as set forth in claim 1, wherein each of said correlators comprises: an inverter circuit section for receiving said straight binary data and outputting inverted data of said straight binary data; an exclusive OR circuit section including a plurality of exclusive OR circuits each receiving one bit of said straight binary data except for a most significant bit of said straight binary data and receiving said most significant bit, and a circuit for generating “1” as a most significant bit output; and a selector, connected to one of said data holding circuits, said inverter circuit section and said exclusive OR circuit section, for selecting one of said straight binary data, said inverted data of said straight binary data and output data of said exclusive OR circuit section in accordance with said 2-bit code.
 4. A code division multiplex access receiver for receiving straight binary input data obtained by an analog/digital conversion of a base band signal generated by demodulating a received signal on a chip rate basis, said receiver comprising a perch search section including a matched filter, said matched filter comprising: a plurality of data holding circuits adapted to sequentially hold said straight binary input data; a plurality of correlator, each connected to one of said data holding circuits, each of said correlators receiving one bit of a known scrambling code and one bit of a scrambling code selected by a base station as a 2-bit code outputting said straight binary input data as it is when said 2-bit code is “00”, outputting said straight binary input data after logically inverting said straight binary input data when said 2-bit code is “11”, and outputting exclusive OR values between said straight binary input data except for its most significant bit thereof and said most significant bit while outputting “1” for said most significant bit when said 2-bit code is one of “01” and “10”; an adder, connected to said correlators, for adding output signals of said correlators and outputting an addition result as a correlation value.
 5. The receiver as set forth in claim 4, wherein each of said data holding circuits comprises a dynamic flip-flop circuit.
 6. The receiver as set forth in claim 4, wherein each of said correlators comprises: an inverter circuit section for receiving said straight binary input data and outputting inverted data of said straight binary input data; an exclusive OR circuit section including a plurality of exclusive OR circuits each receiving one bit of said straight binary input data except for a most significant bit of said straight binary input data receiving and said most significant bit, and a circuit for generating “1” as a most significant bit output; and a selector, connected to one of said data holding circuits, said inverter circuit section and said exclusive OR circuit section, for selecting one of said straight binary input data, said inverted data of said straight binary input data and output data of said exclusive OR circuit section in accordance with said 2-bit code.
 7. The receiver as set forth in claim 4, wherein the number of sets of said correlators and said adder is made equal to the number of types of scrambling codes that can be used by said base station.
 8. The receiver as set forth in claim 4, wherein said matched filter is adapted to input different ones of scrambling codes possibly being used by said base station to said correlators and to determine a correlation simultaneously for all said correlators to receive an obtained correlation value from said adder and identify a scrambling code being used by said base station. 